1. Field of the Invention
The present invention relates to a field emission display (FED) in which the field emission device is applied to a flat display, and in particular, to the field emission display in which a gate plate having a gate hole and a gate electrode around the gate hole is formed between an anode plate having phosphor and a cathode plate having a field emitter and a control device for controlling field emission current, wherein the field emitter of the cathode plate is constructed to be opposite to the phosphor of the anode plate through the gate hole.
2. Background of the Related Art
A field emission display is a device representing an image through cathodeluminescence of a phosphor, by colliding electron emitted from the field emitter of a cathode plate against the phosphor of an anode plate, wherein the cathode plate having the field emitter and the anode plate with the phosphor are formed to be opposite to each other by vacuum packaging with them separated by a given distance (for example, 2 mm). Recently, many researches and developments have been made on the field emission display as the flat display capable of replacing the conventional cathode ray tube (CRT). Electron emission efficiency in the field emitter being a kernel constitutional element of the field emission display is variable depending on a device structure, an emitter material and a shape of the emitter.
The structure of the field emission device can be mainly classified into a diode type having the cathode (or emitter) and the anode, and a triode having the cathode, the gate and the anode. Metal, silicon, diamond, diamond-like carbon, carbon nanotube, and the like are usually used as the emitter material. In general, metal and silicon are manufactured to the triode structure and diamond, carbon nanotube, etc. manufactured to the diode structure.
The diode field emitter is usually formed by making a diamond or a carbon nanotube film-shaped. The diode field emitter has advantages in simplicity of the manufacturing process and high reliability of the electron emission, even though it has disadvantages in controllability of the electron emission and low-voltage driving, compared with the triode field emitter.
Hereinafter, a conventional field emission display having field emitters will be described with reference to the accompanying drawings.
FIG. 1 is a perspective view schematically illustrating the construction of a conventional field emission display having a diode field emitter.
A cathode plate has cathode electrodes 11 arranged in a belt shape on a lower glass substrate 10B and film-shaped field emitter materials 12 on a portion of there. An anode plate has transparent anode electrodes 13 arranged in a belt shape on an upper glass substrate 10T and phosphors 14 of red (R), green (G) and blue (B) on a portion of there. The cathode plate and the anode plate are vacuum packaged in parallel, while facing each other, by means of using spacers 15 as a supporter. The cathode electrodes 11 of the cathode plate and the transparent anode electrodes 13 of the anode plate are arranged to intersect each other. In the above, an intersecting region is defined as one pixel.
In the field emission display shown in FIG. 1, the electric field required for electron emission is given by the voltage difference between the cathode electrodes 11 and the anode electrodes 13. It has been noted that electron emission usually occurs in the field emitter when the electric field is applied to the field emitter material in the value more than 0.1 V/μm.
FIG. 2 shows the field emission display that was proposed in order to improve the disadvantages of the field emission display shown in FIG. 1, which schematically illustrates the construction of a conventional field emission display using a control device for controlling the field emitter in each pixel of the cathode plate.
The cathode plate includes a belt shaped scan signal line 21S and a data signal line 21D, which are formed of a metal on a glass substrate 20B and capable of an electrical row/column addressing, a film (thin film or thick film) shaped field emitter 22, in which each pixel defined by the scan signal line 21S and the data signal line 21D is formed of diamond, diamond-like carbon, carbon nanotube, etc., and control devices 23 connected to the scan signal line 21S, the data signal line 21D and the field emitter 22 to control a field emission current depending of the scan and the data signals of the display. The anode plate includes transparent anode electrodes 24 arranged in a belt shape on a glass substrate 20T and phosphors 25 of red (R), green (G) and blue (B) on a portion of there. The cathode plate and the anode plate are vacuum packaged in parallel, while facing each other, by means of using spacers 26 as a supporter.
In the field emission display shown in FIG. 2, a high voltage is applied to the anode electrodes 24 to induce electron emission from the film-shaped field emitter 22 in the cathode plate and to accelerate the emitted electrons with high energy at the same time. Then, if a signal of the display is inputted to the control devices 23 through the scan signal line 21S and the data signal line 21D, the control device 23 controls the amount of electrons emitted from the film-shaped field emitter to represent row/column images.
The diode field emitter used for the field emission displays shown in FIG. 1 and FIG. 2, as described above, has advantages that a structure is simple and a manufacturing process is easy, since it does not need a gate and a gate insulating film unlike a conic triode field emitter.
Further, the diode field emitter has very low probability in the breakdown of the field emitter by the sputtering effect upon emission of the electrons, so that it has a high reliability and there is no breakdown phenomenon of the gate and the gate insulator that is very problematic in the triode field emitter.
In the field emission display having the diode field emitter shown in FIG. 1, however, a high electric field necessary for field emission is applied through the electrodes (cathode electrodes 11 and transparent anode electrodes 13 in FIG. 1) of the upper and lower plates that are separated by a significant distance (usually, 200 μm to 2 mm), so that a display signal having high voltage is required. As a result, there is a disadvantage that an expensive high voltage driving circuit is required.
In particular, in the field emission display having the diode field emitter of FIG. 1, although the voltage necessary for electron emission is lowered by reducing the distance between the upper plate and the lower plate, low voltage driving is nearly impossible since the anode electrode 13 is used as the acceleration electrode of the electron as well as the signal line of the display. In the field emission display, a high-energy electron over 200 eV is required to emit the phosphor. The higher electron energy is, the better luminous efficiency is. Thus, a high-brightness field emission display can be obtained only if the high voltage is applied to the anode electrode.
In the conventional active-matrix field emission display having the diode field emitter shown in FIG. 2, the control device 23 of the field emitter is used in each pixel and, by inputting the display signal through it, the active-matrix field emission display can solve the high voltage driving problem in FIG. 1 and the problems such as non-uniformity of electron emission, cross talk, etc. at the same time. The high voltage applied to the anode electrode 24 for the field emission and electron acceleration, however, comes to induce a significant voltage to the control devices 23 of each pixel. And, if the voltage is induced more than the breakdown voltage of the control devices 23, the control device could be failed.
Therefore, the conventional active-matrix field emission display has disadvantages that the voltage that can be applied to the anode electrodes 24 is limited depending on the breakdown characteristics of the control devices 23 and it is difficult to fabricate the field emission display having the high brightness due to the limited anode voltage.